My VTA ST-120 is on the way .....and other loose ramblings of an old fart

btw hope you do another FLIR with the KT88's mounted ^^

Thinking of those myself - Shuguang most likely - from a vendor that does additional burn in and matching thereafter..

When the initial shock of the basic kit expense has subsided for my wife I might do what Skizo did and, over a crate of some belgian beer, get together with my metal working neighbour and make a 19" wide case and matching cage out of 316 ( plus have the other dimensions proportionally correlating to the original case ) which like Skizo said would have it all run substantially cooler - and last longer perhaps..

Roy wrote:https://community.roonlabs.com/t/allo-boss-v1-2-info/33562/17 check out the posts by one of the Allo crew



Not so   pretty imo  but very tidy  and apparently somesort of tie in to the cpu package to conduct heat into the case which then acts as a heatsink
Not out yet - possibly  they knew about the rpi3 b+ changes to the cpu packages with that extra metal lid on it which would need to be accounted for in this case..
Wonder how they  manage to do it with the Boss hat board on top.. heatpipe maybe.   Or  as that case looks like it is in three layers, possibly the middle has an arm reaching out to touch the cpu

FLIRC case has it easy - just an extrusion down onto the cpu..

I have those FLIRC cases. Used them for bunch of Kodi TV boxes I built for friends and family and gave a couple to some very important clients as a Christmas gift.  However, my personal Kodi box is machined from a solid billet of 6061 aluminum and the whole thing is a massive heat-sink ......just because I can  

Roy wrote:btw  hope you do another FLIR with the KT88's mounted ^^

Thinking of those myself - Shuguang most likely - from a vendor that does additional burn in and matching thereafter..  

When the initial shock of the basic kit expense has subsided for my wife I might do what Skizo did and, over a crate of some belgian beer,  get together with my metal working neighbour and make a 19" wide case and matching cage out of 316  ( plus have the other dimensions proportionally correlating to the original case )  which like Skizo said would have it all run substantially cooler - and last longer perhaps..

KT-88's and 12BH7 glassware from Jim McShane are here, biased to 55mA and are sounding AWESOME! .....yes, I will shoot another Flir E8 pic this afternoon ....Hmmmm, I think I really prefer these bottles!

......and, I'm designing something very simple yet aesthetically pleasing and unique for the Rpi/Allo DAC

Here are a couple FLIR shots:

6550 Tubes


KT-88 Tubes

so yeah - hót lol

but I just noticed - the lowest temps measured by the FLIR I assume to be ambient temps
37°C nice ^^

Roy wrote:http://moodeaudio.org/ going to try this one tomorrow

 looks slick

Hey Roy,
How did this work out for you?

Wife made me work on my quota of going through my stuff n making boxes of ebay/goodwill/recycling center  - we're planning on moving house - so  still havent made another sd card with this installed on it - the weekend is almost here though! Don't expect any surprises - the Boss is fully supported in it, and the interface is how I like it - tidy and not gaudy.

and my rummagings yielded a box full of sd cards and alike I didn't know I had =S


So   were the FLIR readings to yóur satisfaction Cletus?

Yup, now that she's been running a bit, the KT-88s took the power transformer temp up by 6*C so it's steady now at max 77*C
BTW   .....the KT-88s sound wonderful!  .....even with streaming lower quality audio from "Alexa". Bob has created a great amp for us !

CletusB wrote:Yup, now that she's been running a bit, the KT-88s took the power transformer temp up by 6*C so it's steady now at max 77*C
BTW   .....the KT-88s sound wonderful!  .....even with streaming audio from "Alexa"

That's normal, at least it was with me. Temps and bias will wander around for awhile the first 100 hours or so.

Cletus   you strike me as the sort of person who would come up with a sensible answer to this one so here is a question ;

With a solid state rectifier in place the capacitance of the reservoir capacitors could go much higher ( as to why the added capacitance would be unwelcome after a tube rectifier I welcome the explanation  also ^^ )
and eying the standard st-120’s two 180microfarad 350V caps connected in series with resistors  making a total of 180 for the reservoir  I wonder wether this ís something to look into and  just how high it could  or should be with a Weber coppercap in place..

Roy wrote:Cletus   you strike me as the sort of person who would come up with a sensible answer to this one so here is a question ;

With a solid state rectifier in place the capacitance of the reservoir capacitors could go much higher ( as to why the added capacitance would be unwelcome after a tube rectifier I welcome the explanation  also ^^ )
and eying the standard st-120’s two 180microfarad 350V caps connected in series with resistors  making a total of 180 for the reservoir  I wonder wether this ís something to look into and  just how high it could  or should be with a Weber coppercap in place..

Serial connetion of caps will reduce the capacitance

Say Cx = ( C1 * C2 ) / ( C1 + C2 )
For equal caps the capacitance of 2 caps in series will be half. In this case 90uF

Still, upping the cap in an amp will not add much more then the cost of caps. Hum can only
be reduced to inaudibility and the power peaks has to be supplied by the mains.

oh yes forgot to half the capacitance due to the series ^^   While I was typing I was thinking it but then my hands got the better of me lol

Well from what I understand of things Peter - see above for the extent lol - besides smoothing out things those caps also store energy for the amp circuits to tap - the mains supplies the energy yes but those caps will store reserves to tap for transients.. The power flows through those caps, but they retain the capacity for short bursts of power which exceed the flow going through them - and for some reason  tube rectifiers do not like too much capacitance attached, but the ss types can handle much more and  having more on tap means  more energy for transients

hm   sick kid to the left of me  sick wife to the right  and my brain is feeling foggy too so   forgive me ^^

Add another thing to my todo list the coming week - reading glasses..

Peter is quite correct above.  
May I add:
Apart from filtering the power supply (and you soon reach a point of "saturation") the capacitors store a reserve of energy for the amplifier to tap on during transients (like when that kick-drum gets slammed). During that transient peak, the potential energy available to drive that woofer cone is the sum of what the transformer/rectifier is capable of delivering, plus what's stored in the sum capacitance (like having two power supplies in parallel). Immediately after that transient, the transformer/rectifier must very quickly recharge what was previously depleted from reproducing that "kick-drum thud" and make ready for the next transient we're about to throw at it. At that recharge instant, the capacitor bank presents a very low impedance to the rectifier/transformer and there is massive current flow to try to bring the power level back up to full snuff in the capacitor.
Tube rectifiers in essence may be thought of as having a virtual "resistor" in series with them, giving some sag in the delivered power (Weber tries to replicate this to an extent in their WZ68 for example, by including a physical power resistor in series with the solid-state diodes). Silicon diodes in forward bias (conducting) have a very low impedance as compared to a tube rectifier. Silicon diodes can recover quite readily and deliver that "recharge" to the capacitors with much more aggressive capability than a tube.
Tubes like the KT-88 and KT-120, etc. Can be quite demanding on the power supply (transformer, rectifier and capacitor bank).
In the power supply design of the ST-120, the rectifier is first introduced to a much milder capacitance (40uF) before progressively going to more aggressive filtering via the chokes and series resistors. This is especially important if that tube rectifier is to survive.
Well, I hope this made some sense, cause I have not yet had my morning coffee. Maybe Bob or some other more knowledgeable person than I may chime in and correct me as necessary.  At the end of the day, an amplifier IS a beefy POWER SUPPLY modulated by the input signal

FOOTNOTE: I think the "Yellow Sheet Mod" is an excellent upgrade, as those two silicon diodes take the brunt of the rectification duty off the tube rectifier, while the tube still provides the desired sag and response characteristics (tubiness) we so crave.

Thanks Peter and Cletus - goes a ways towards me understanding things!

As for the tube rectifier - I see too many guitars in your profile pic Cletus ^_^ suspect at some point you will be hooking one up to the 120 and then that sag is something you would want and while playing adding that depth to the feel you get     but when I play back something beefy out of my collection I like the amp to rumble without a grumble so  a Weber WS1 and the TDR board is on the list

Not a purist - I've had SS gear most of my life save for when I was a kid and the memory of that tube radio is like magic in my memory - why I set my sights on the VTA now ^^
but seeing as how the SS rectifier will cut down on cost and enable more headroom for the actual musical reproduction it seems like a good choice to me to make

My current little beast running things:

Roy wrote:Thanks Peter and Cletus - goes a ways towards me understanding things!

As for the tube rectifier - I see too many guitars in your profile pic Cletus ^_^ suspect at some point you will be hooking one up to the 120 and then that sag is something you would want and feel while playing adding that depth to the feel you get playing    but when I play back something beefy out of my collection I like the amp to rumble without a grumble so  a Weber WS1 and the TDR board is on the list

The system in a nutshell:
The guitars and amplifier shown have always been my dream equipment (Fender Jaguar, Fender Starcaster and Fender Silverface 1974 Twin Reverb amp - Blackface modified).  
There is a single octave Oxygen 25 Midi keyboard too.
The recording/playback/mastering console is a mix-match of stuff centered around Band in a Box, Cakewalk and the GNX3 Guitar Workstation.
My go-to live/recording mics are the Sure SM-57 and the Audio Technica AT-3525 studio mic.
After the vocal mic there is usually a TC-Helicon HarmonyG-XT Vocal Processor to sweeten things up a bit and create harmonies when needed.
The studio near-field monitors are the very affordable, but nice (IMHO) Edifier powered R1280T.
Studio headphone monitors are AKG K44s.
Mixing board (the gateway to the recording system) is Behringer Xenix 1202FX
Optiplex 755 PC maxed-out with memory and hard drives and a M-Audio Audiophile Sound Card running Windows 7.
Preamp intervention in all that is my own design 12AX7 build / solid-state tone stack with a Pass Labs J-FET buffer.
The output from the Preamp can indeed be readily routed via an A/B selector to the ST-120 / A7s or the Edifiers.
Quite a versatile little home recording rig, if I do say so myself.
Of course Rome was not built in a day, so this has been a labor of love (and sometimes frustration) spanning many years!
BTW the EQ pictured was never in-circuit but used only for the Spec-analyser display with a calibrated Leader Mic and a home-brew pink noise generator (it is now out the door ....too many nice pc-based, FFT spec analyzers out there).

Said it before - wish my son had a grandpa like you ^^ and again dont mean to cast asperions at your age   Very nice kit

If you ever think about other monitors on your desk - have a gander at the Kef Q100
I got those on mine - co-incidental woofer and tweeter system. Not powered mind you but  as nearfields  they are reAlly nice for the price - payed 200 for this pair as they are yesterday's model. Kef reworked the driver a little bit  and decided on a rear ported update with the Q150 which is less than optimal close to a wall. Amazing amount of low end for its size, vocals are  wonderful. Not a whole lot of treble way up top but at my age thats not a terrible shame - not that its bad at all but it does taper off starting round 17k or so from memory. With the drivers being coincidental you get an amazing width and depth and   'thereness'. The frequency response is pretty good but if you want flat - Equalizer APO ( infinite band EQ with really low latency) program and some corrections with a mic would yield a darn flat graph with these things.

Roy wrote:Said it before - wish my son had a grandpa like you ^^ and again dont mean to cast asperions at your age  ........

Hahahah NO PROBLEM ....I've long come to terms with my being an "Old Fart"
BTW First grand child expected any day now and I'm working with my son (the new daddy to be) to develop an ST-120 based system for his home .....he's at the stage of over-thinking all the equipment specs and measurements, but we're getting there ....being the PhD Molecular Biologist scientist that he is

What do you guys think of the ELAC Debut F6 as a cost effective entry point speaker system for use with an ST-120 and a DAC

A ways back when the Unifi came out  was not too impressed by it - hence the Kef here now..
That Q lineup from yesteryear is going   pretty cheap these days - Q500 would be a steal at the prices they've gone at here
( I've seen em go for 500 a pair new in the box ) Successor is the Q550 those would have a going price per pair about the same
as that elac - my bet is the kefs will knock the socks off the elac - especially when the volume goes up a bit those other unifis I heard
were not pleasing.

and it has that bit of umpf for a larger space

..and very nice w the grandkid =] You're going to get it busy lol

Roy wrote:A ways back when the Unifi came out  was not too impressed by it - hence the Kef here now..
That Q lineup from yesteryear is going   pretty cheap these days - Q500 would be a steal at the prices they've gone at here
( I've seen em go for 500 a pair new in the box ) Successor is the Q550   those would have a going price per pair about the same
as that elac - my bet is the kefs will knock the socks off the elac - especially when the volume goes up a bit those other unifis I heard
were not pleasing.

and it has that bit of umpf for a larger space

Investigate Tyler Acoustics in Kentucky as well. Last speaks I'll ever buy, and very ~90 dB efficient. Hand-made to order and worth 4x the retail stuff.
Oops, forgot you're in Europe. Still, talk to Tyler Lashbrook about shipping. It's free in N. America, maybe he can cut you a deal on the slow boat. Well worth the wait.

Roy wrote:..and very nice w the grandkid =]  You're going to get it busy lol

They're in the States and I'm here in Trinidad ....will go over n visit soon ...maybe build the ST-120 while I'm over there visiting ...certainly want the grandkid growing up with quality audio around

Both of those speakers deserve at least an audition, before buying anything.

Oooooooh! The Tyler stuff certainly looks extremely impressive, but way out of his price range at this time.

They do - the real test is where they are intended to live though eh - and ofcourse the WAF ^^

I bought a pair of B&W Matrix 3's before I met my wife - lovely beasts. Pretty big and not too pretty in her opinion though.. They grated on her - too big! Determine the layout of the livingroom too much! etc.. Over the years I tried some other speakers but they always returned to the livingroom.. Couple of years ago came across a pair of Kef Reference Model Three Two. They had been painted a very nice white by the owner - he ran a car body repair shop so the paint job is top notch though. They came home, are a good head taller than the B&W's and sound fantastic here.
She was pleased =]
Húge targets for the little godzilla here though lol.. so every now and then I mentioned maybe we should sell them on, get some smaller speakers with a sub or something - but these days she says no! they are staying! =D

These days Kef offers all white speakers on much of their lineup ^^